Abstract: TRULI, also known as Lats-IN-1, is a pharmacological inhibitor of the LATS1/2 kinases, which are core components of the highly conserved Hippo signaling pathway. By inhibiting LATS1/2, TRULI prevents the phosphorylation and subsequent degradation of Yes-associated protein (YAP), allowing it to translocate to the nucleus and drive gene transcription associated with cell proliferation, survival, and plasticity. Recent studies have explored the therapeutic potential of TRULI across various regenerative and pathological contexts. In cardiovascular research, TRULI has demonstrated significant efficacy in protecting cardiac function, reducing infarct size, and promoting cardiomyocyte proliferation following myocardial infarction. In dental research, it has been shown to induce proliferation and spheroid formation in dissociated primary ameloblasts and dental epithelial progenitors. Conversely, in corneal studies, TRULI was found to inhibit the de-differentiation of corneal epithelial cells into limbal epithelial stem cells, highlighting the highly context-dependent nature of YAP activation. This review synthesizes the current literature on TRULI, detailing its pharmacological activity, molecular mechanisms, limitations, and future perspectives in regenerative medicine and targeted therapies.
1. Introduction
The Hippo signaling pathway is an evolutionarily conserved kinase cascade that plays a critical role in organ size control, tissue regeneration, and repair by regulating cell proliferation, apoptosis, and stem cell self-renewal [2]. A central mechanism of this pathway involves the MAP4K/MST1/2-LATS1/2 kinase cascade, which negatively regulates the transcriptional co-factor Yes-associated protein (YAP) [1]. TRULI, frequently referred to in the literature as Lats-IN-1, is a small molecule inhibitor specifically targeting LATS1/2 kinases [1][2]. By blocking LATS1/2 activity, TRULI modulates the Hippo pathway and its downstream effects, presenting a novel and accessible translational approach for regenerative medicine and disease treatment [2]. While the mammalian heart and other specialized tissues often have limited regenerative capacity, pharmacological agents like TRULI offer a strategy to manipulate cell proliferation and plasticity under various physiological and pathological conditions [1][2].
2. Pharmacological Activity
TRULI (Lats-IN-1) exhibits diverse pharmacological activities across different tissue types, primarily characterized by its ability to stimulate cell proliferation and modulate cellular plasticity:
Cardiac Regeneration and Repair: In murine models of myocardial infarction (MI), intraperitoneal administration of Lats-IN-1 (1 mg/kg/d) significantly alleviates cardiac dysfunction. It improves systolic function, evidenced by enhanced ejection fraction (EF%) and fractional shortening (FS%), and reduces pathological ventricular dilation [2]. Furthermore, Lats-IN-1 reduces the size of the myocardial infarct and mitigates cardiac fibrosis. Crucially, it promotes the proliferation of cardiomyocytes in both the infarcted and remote zones of the heart, as indicated by increased markers such as PH3, Aurora B kinase, and BrdU incorporation [2].
Dental Epithelial Cell Plasticity: In the context of dental tissue, TRULI (used at 10 μM in 3D culture) induces proliferation in primary differentiated dental epithelial cells. When cells from the ameloblast region or cervical loop are dissociated and cultured in Matrigel, TRULI treatment significantly enhances their spheroid-forming capacity. This demonstrates that LATS inhibition can confer progenitor-like proliferative plasticity to differentiated ameloblasts when they are removed from the intact tissue microenvironment [1].
Corneal Epithelial Stem Cell Modulation: Interestingly, TRULI exhibits an inhibitory effect in certain regenerative contexts. During the regeneration of limbal epithelial stem cells (LESCs) following innate stem cell ablation, the topical administration of TRULI (20 μM) inhibited the de-differentiation of corneal epithelial cells (CECs) into LESCs *in vivo*. This contrasts with YAP-TEAD inhibitors, which promoted this specific de-differentiation process, suggesting that LATS-dependent suppression of YAP is actually required for CEC de-differentiation [3].
Other Applications: Literature also notes the use of Lats-IN-1 in osteoarthritis to block NFκB activation and prevent the upregulation of inflammatory genes in chondrocytes subjected to mechanical stress. Additionally, it has been utilized in oncology research (at doses of 10 mg/kg) to suppress adverse biological characteristics of breast cancer through Hippo pathway modulation [2].
3. Molecular Mechanism of Action
The primary molecular mechanism of TRULI (Lats-IN-1) is the direct inhibition of LATS1 and LATS2 kinases. Under normal homeostatic conditions, active LATS1/2 phosphorylates YAP at specific serine residues (e.g., Ser112 and Ser381 in mice), leading to YAP's cytoplasmic sequestration and degradation [1]. By inhibiting LATS1/2, TRULI prevents this phosphorylation. Consequently, unphosphorylated (active) YAP accumulates and translocates into the nucleus, where it interacts with transcription factors (such as TEAD) to drive the expression of downstream genes critical for cell proliferation, survival, and stem cell self-renewal [1][2][3].
In cardiac tissue post-MI, Western blot analyses confirm that Lats-IN-1 treatment decreases the phosphorylation levels of both LATS1/2 and YAP. This activation of YAP is accompanied by a marked reduction in apoptotic signaling; Lats-IN-1 decreases the expression of the pro-apoptotic marker Bax and reduces the levels of apoptosis-executioner proteins Caspase 3 and Caspase 9, thereby protecting cardiomyocytes from apoptosis [2].
4. Structure-Activity Relationship (SAR)
The provided literature focuses extensively on the biological and translational applications of TRULI (Lats-IN-1) in tissue regeneration and cellular plasticity. However, specific chemical structure details, functional group modifications, and comprehensive Structure-Activity Relationship (SAR) data for the compound are not detailed in the provided texts [1][2][3]. Future chemical and pharmacological studies are required to elucidate the precise molecular interactions between TRULI and the LATS1/2 kinase domains.
5. Current Limitations
Several limitations currently restrict the broader clinical application of TRULI:
Lack of Dose-Response Data: Current *in vivo* studies have utilized fixed doses (e.g., 1 mg/kg/d for cardiac repair, chosen for cost and side-effect considerations, compared to 10 mg/kg used in breast cancer models). There is a critical lack of comprehensive dose-response analyses to determine the optimal therapeutic window, efficacy, and safety profile of Lats-IN-1 at varying concentrations [2].
Context-Dependent Efficacy: The effects of YAP activation via TRULI are highly dependent on the cell type and tissue microenvironment. For instance, while TRULI successfully induces proliferation in dissociated ameloblasts *in vitro*, YAP overactivation fails to induce proliferation in intact dental tissue *in vivo* due to local inhibitory signals like contact inhibition [1]. Furthermore, in the cornea, TRULI actually inhibits the necessary de-differentiation of CECs into stem cells, proving that YAP activation is not universally beneficial for all regenerative processes [3].
Complex Signaling Crosstalk: The Hippo pathway is modulated by a vast network of upstream inputs, including mechanical stress, tissue stiffness, and cell adhesion. The exact mechanisms by which TRULI interacts with these mechanotransduction pathways (such as those altered by tissue scarring or chemical burns) remain incompletely understood [3].
6. Future Perspectives
TRULI (Lats-IN-1) holds significant promise as a novel therapeutic strategy across multiple disciplines. In cardiovascular medicine, it represents a highly translational approach to enhance endogenous cardiac regeneration, reduce fibrosis, and improve outcomes for patients suffering from heart failure and myocardial infarction [2]. In orthodontics and craniofacial research, the ability of TRULI to modularly control the proliferation of progenitor and differentiated cells offers potential pathways for safe, stem cell-based dental treatments and tissue engineering [1].
Future research must focus on elucidating the upstream inputs and downstream targets of YAP that dictate its context-dependent roles. Advanced techniques such as single-cell RNA-sequencing and spatial transcriptomics will be vital to understanding how LATS inhibition alters lineage specification [1]. Additionally, rigorous pharmacological profiling, including dose-response and long-term safety studies, will be essential before TRULI can be transitioned from experimental models to clinical applications in regenerative medicine and oncology [2].
